1. Field of the Invention
This invention relates to a process and apparatus for controlling undesirable emissions from a coke oven and, in particular, to capturing and controllably removing particulate and gaseous emissions that evolve from hot coke as it is pushed from a coke oven in the operation of a coke battery.
2. Description of the Prior Art
Generally speaking, coke side sheds are available that are reasonably effective in controlling coke emissions during the pushing operation. Few people who are knowledgeable about coke side systems will dispute this fact. The prime factor for their limited use in the steel industry has been the adverse environmental conditions created for the workers underneath the shed. Accordingly, the evolution or development of improved shed designs has been directed more toward enhancing the working conditions inside the shed, rather than the mere emission capture aspect of the operation.
The poor working conditions are a result of particulate fallout which occurs during the pushing of the coke into the quench car. Initial designs of sheds were such that emissions were allowed to rise and expand in essentially an open room without regard to particulate fallout. Although improvements have been made to the design of sheds through the use of deflector plates and expansion chambers, particulate fallout and related problems persist to the point where coke plants are still reluctant to use sheds for emission control.
In order to more fully appreciate the advantages of this invention over previous shed designs, several factors must be examined. First, one must understand the flow characteristics of the emissions in a shed. Once the hot emissions rise in the shed they expand longitudinally as well as laterally and, in particular, vertically, and hover in the peak or apex of the shed until evacuation through the fume main takes place. This means there are gaseous and particulate emissions in areas of the shed that are not aided by a thermal draft or thermal drive to keep the particles suspended in the gas. These areas contribute heavily to the fallout problem due to the fact that there is no longer a flow condition to keep the particles entrained or airborne. The same condition exists in the pushing area of the shed once the push is complete and the quench car begins its travel to the quench station. The thermal draft is minimized and fallout can increase.
Accordingly, it is essential to the shed designer to provide for an expansion chamber that is located at a maximum reasonable distance from or, at least, outside the quench track and bench area. Prior shed designs, most notably those of U.S. Pat. Nos. 3,972,782, 3,937,656 and 3,844,901, employ a flow path restriction that will accelerate the emissions into an expansion zone or the like. However, it should be noted that on each of the foregoing designs the throat section or flow path restriction area is on a horizontal plane or at a 45 degree slope. The significance here is that part or all of the expansion area is over top of the throat section which means that, when the emissions expand longitudinally, fallout is vertical and back on the quench track and bench area.
The present invention comprises a significant improvement over such prior art designs by placing the expansion chamber at a maximum reasonable distance from or, at least, outside the bench area and the quench track or, more particularly, at least as far removed as the outer boundary for the pushed coke. The plane of the throat section which separates the initial containment or entrapment chamber from an adjacent, longitudinally parallel expansion or second containment chamber is on a vertical or substantially vertical plane. This means that any fallout occurring in the expansion zone or chamber cannot fall back into the initial entrapment chamber and thus on the workers.
In order for fallout prevention to occur effectively, the emissions must be conveyed to the expansion chamber with a minimum degree of expansion. Thus, the sloped roof of this invention, which spans the first containment or entrapment chamber, has a dual purpose or function. One is to act as a cover for this portion of the shed and, second, it is a linear directional vane for channeling the emissions away from the bench area before they have a chance to expand. The roof slope is preferably approximately 20 to 50 degrees, depending on the application. In contradistinction, the shed designs of U.S. Pat. Nos. 3,972,782, 3,937,656 and 3,844,901 have roof slopes or curvatures that adversely project both inwardly and outwardly in relation to the battery. Moreover, in U.S. Pat. Nos. 3,972,782 and 3,937,656 a heat shield or baffle plate slopes inwardly directing the emissions back towards the bench area and in U.S. Pat. No. 3,844,901 the emissions are directed to a fume main which is unobstructedly positioned directly over the quench tracks and, thus, establishes the fallout area for particulates directly over an area usually occupied by coke oven workers.
Other factors must also be considered in connection with the location of the fume duct. The location of the fume duct is most important for removing emissions effectively, quickly and economically. The fume duct should be located at the apex or peak of the expansion chamber for greatest removal capabilities. If the fume duct is located as shown in U.S. Pat. No. 3,972,782, the exhaust fan horsepower requirements must be higher to overcome the extra flow resistance due to the numbers of 90 degree turns the gaseous emissions must make to enter the duct. Also, there is added resistance in overcoming the thermal draft of the gases by trying to pull the gases from a higher elevation to a lower elevation.
Another disadvantage of the shed of U.S. Pat. No. 3,972,782, is that, if there are leaks in the roof or siding, the ability to pull the emissions to the exhaust duct would be greatly hampered. The flow path of the gas emissions is of great importance to the shed designer. Thus, in accordance with the present invention, the flow path of the gas emissions does not pass through the fallout or settling chamber. This aspect of the design is beneficial because it eliminates the possibility of re-entrainment of fallout particles in the gas stream. This means fewer particulates in the gas stream to the gas cleaning system. By maximizing and controlling the fallout particles in a suitable area, such as a defined fallout chamber, the workload of the gas cleaning system, which is normally a high energy user, is lowered. If the gas cleaning system is a baghouse, this means a lower differential pressure across the bags (HP savings), fewer cleaning cycles per day for the bags and increased bag life. In both the shed designs of U.S. Pat. Nos. 3,972,782 and 3,844,901, the flow path of the gas emissions must pass through the expansion and fallout chamber or chambers.
Another important feature of the present invention is the fallout chamber, which is self-cleaning and does not require a mechanical system to remove the particulate fallout. The fallout chamber allows the particles to slide along the sloped bottom section (50 degrees or greater) and eventually to the ground, across the tracks from the bench area, where routine maintenance is performed regardless of whether a shed exists or not. This feature is important in that there are no appreciable areas for dust build-up in the shed. All sloped areas or sections should be 50 degrees or greater (the minimum recommended chute angle for coke breeze is 50 degrees). Both the shed designs of U.S. Pat. Nos. 3,972,782 and 3,844,901 have areas for dust build- up. The design of U.S. Pat. No. 3,972,782 must mechanically remove fallout from the hopper area and that of U.S. Pat. No. 3,844,901 has a catch basin behind the heat shield-deflector plate for dust build-up.